1. Field of the Invention
This invention relates to conversion of digital video signals from a conventional format to a high-definition format and/or vice versa.
2. Description of the Prior Art
High definition digital video is becoming increasingly popular, and common formats for the video signals are:
SMPTE 240M format, which is characterised by 1125 lines, 60 field/s, 2:1 interlace, with a 16:9 aspect ratio and 1920.times.1035 active pixels per frame; and PA0 European HDTV format, which is characterised by 1250 lines, 50 field/s, 2:1 interlace, with a 16:9 aspect ratio and 1920.times.1152 active pixels per frame. PA0 CCIR 601 525-line format, which is characterised by 525 lines, 60 field/s, 2:1 interlace, with a 4:3 aspect ratio and 720.times.486 active pixels per frame; PA0 CCIR 601 625-line format, which is characterised by 625 lines, 50 field/s, 2:1 interlace, with a 4:3 aspect ratio and 720.times.576 active pixels per frame; PA0 4fsc 525 D2 format, which is characterised by 525 lines, 60 field/s, 2:1 interlace, with a 4:3 aspect ratio and 768.times.486 active pixels per frame; and PA0 4fsc 625 D2 format, which is characterised by 625 lines, 50 field/s, 2:1 interlace, with a 4:3 aspect ratio and 948.times.576 active pixels per frame.
More and more material is being originated in these formats for processing and/or distribution in them. However, there is obviously a great bulk of material which has been originated, or still needs to be originated, in conventional definition format, and there is a desirability to be able to up-convert such material to high definition format so that it can be integrated with other high definition material and/or so that it can be distributed in high definition format. Furthermore, material which is now being originated in high definition format may need to be converted to conventional definition format so that it can be integrated with other conventional definition material and/or so that it can be distributed in conventional definition format. Examples of conventional definition digital formats are:
(Although 60 field/s is mentioned above as the field rate for the 525-line formats, strictly the field rate should be 59.94 field/s. Nevertheless, for simplicity in this specification the value of 60 field/s is used.)
Problems associated with such conversion include dealing with the change of aspect ratio between 4:3 for the conventional definition formats and 16:9 for the high definition formats, in addition to dealing with the changes of resolution, which are different in the horizontal and vertical directions.
U.S. Pat. No. 5,208,669 (corresponding to GB 9100314.5 filed Jan. 8, 1991) hereinafter referred to as "the first earlier application" describes an apparatus for up-converting a digital video signal from a first definition format to a second higher-definition format, comprising: storage means which can store an input field/frame of pixel data in the first format; storage control means for controlling the storage means to output the stored pixel data together with dummy data as an intermediate field/frame in the second format, such that the pixel data occupies a continuous active portion of the intermediate field/frame and the dummy data occupies the remainder of the intermediate field/frame; and means for processing the intermediate field/frame by expanding the active portion thereof in the vertical and horizonal directions and producing an output field/frame in the second format such that the pixel data extends across substantially the whole of the output field/frame in at least one of the two directions.
The apparatus of the first earlier application is of particular application in converting digital video signals between formats having different aspect ratios, and in this case the processing means may be arranged to be operable in a side-bar mode to expand the active portion of the intermediate field/frame to an extent such that the active portion extends across substantially the whole of the output field/frame in one of the directions and such that the dummy data occupies at least one marginal portion of the output field/frame. Alternatively or additionally, the processing means may be arranged to be operable in an edge-crop mode to expand the active portion of the intermediate field/frame to an extent such that the active portion extends across substantially the whole of the output field/frame in one of the directions and across more than the output field/frame in the other direction so that at least one marginal portion of the active portion is cropped. Alternatively or additionally, the processing means may be arranged to be operable in a zoom mode to expand the active portion of the intermediate field/frame to an extent such that the active portion extends across more than the whole of the output field/frame in one of the directions and across less than or more than the output field/frame in the other direction. Preferably, the processing means is operable in the side-bar, edge-crop or zoom mode, as the case may be, to expand the intermediate field/frame with different horizontal and vertical expansions such that the ratio of the horizontal to vertical expansion is equal to the ratio of the pixel aspect ratio of the first format to that of the second format. Alternatively or additionally, the processing means may be arranged to be operable in a titles mode to expand the active portion of the intermediate field/frame to an extent such that the active portion extends across substantially the whole of the output field/frame in both of the directions without any substantial cropping of the active portion. The processing means may include means to select operation in any one of the modes.
In one embodiment described in the first earlier application, in which the storage means can store a field/frame of pixel data in the second format, and the storage control means includes means to select writing to and reading from the storage means and means for generating addresses for the storage means; the address generating means is operable, (a) when writing is selected, to generate addresses sequentially for the active portion of storage means corresponding to a field/frame in the first format, and (b) when reading is selected, to generate addresses sequentially corresponding to a field/frame in the second format; and the storage means stores the dummy data at addresses not in the active portion thereof.
In an alternative embodiment described in the first earlier application, in which the storage control means includes means to select writing to and reading from the storage means, and means for generating addresses for the storage means, the address generating means is operable (a) when writing is selected, to generate addresses sequentially for the field/frame of pixel data, and (b) when reading is selected, to generate intermittently lines of addresses corresponding to lines of addresses of the field/frame in the first format. The storage control means is operable to output partial lines of the dummy pixel data between the generation of one line of addresses and the next, and to output lines of the dummy pixel data between the generation of one field/frame of addresses and the next. This embodiment has the advantage that the size of the storage means is related to the number of pixels in a field/frame in the first format, rather than the larger number of pixels in a field/frame in the second format.
In either of these embodiments described in the first earlier application, a further such storage means may be provided, with the storage control means controlling the two storage means such that while one is being written to, the other is being read from, and vice versa. This has the advantage that, at least for some types of conversion, the apparatus can operate continuously.
Also, with any of these embodiments, the apparatus may be arranged so that when writing of the, or one of the, storage means is selected, the addresses for that storage means are generated at the pixel rate of the first format; and when reading of the, or one of the, storage means is selected, the addresses for that storage means are generated at the pixel rate of the second format. This enables real-time operation of the apparatus.
The first earlier application also presents a method of up-converting a digital video signal from a first definition format to a second higher-definition format. The method comprises the steps of storing an input field/frame of pixel data in the first format; reading the stored pixel data interspersed with dummy data as an intermediate field/frame in the second format, such that the previously stored pixel data occupies a contentious active portion of the intermediate field/frame and the dummy data occupies the remainder of the intermediate field/frame; and expanding the active portion of the intermediate field/frame in the vertical and horizonal directions and producing an output field/frame in the second format such that the previously stored pixel data extends across substantially the whole of the output field/frame in at least one of the two directions.
U.S. patent application Ser. No. 07/907,315 filed on Jul. 1, 1992 (corresponding to GB 9114706.6 filed on Jul. 8, 1991) hereinafter referred to as "the second earlier application" describes an apparatus for down-converting a digital video signal from a first definition format to a second lower-definition format, comprising: means for processing an input field/frame by compressing the active portion thereof in the vertical and horizonal directions to produce an intermediate field/frame in the first format in which the active portion occupies only part of the field/frame; storage means which receives the intermediate field/frame of pixel data in the first format; storage control means for controlling the storage means to store at least part of the active portion of the intermediate field/frame and to output the stored pixel data as a field/frame in the second format, such that the pixel data of the active portion extends across substantially the whole of the output field/frame in at least one of the two directions. The apparatus is of particular application in converting digital video signals between formats having different aspect ratios, and in this ease the processing means may be arranged to be operable in a letter-box mode to compress the active portion of the input field/frame to ail extent such that the active portion extends across substantially the whole of the output field/frame in one of the directions and such that dummy data occupies at least one marginal portion of the output field/frame. Alternatively or additionally, the processing means may be arranged to be operable in an edge-crop mode to compress the active portion of the input field/frame to an extent such that the active portion extends across substantially the whole of the output field/frame in one of the directions and across more than the output field/frame in the other direction so that at least one marginal portion of the active portion is cropped. Alternatively or additionally, the processing means may be arranged to be operable in a zoom mode to compress the active portion of the input field/frame to an extent such that the active portion extends across more than the whole of the output field/frame in one of the directions and across less than or more than the output field/frame in the other direction. Preferably, the processing means is operable in the letter-box, edge-crop or zoom mode, as the case may be, to compress the input field/frame with different horizontal and vertical compressions such that the ratio of the horizontal to vertical compression is equal to the ratio of the pixel aspect ratio of the first format to that of the second format, so that the picture geometry is preserved. Alternatively or additionally, the processing means may be arranged to be operable in a titles mode to compress the active portion of the input field/frame to an extent such that the active portion extends across substantially the whole of the output field/frame in both of the directions without any substantial cropping of the active portion. In this case, the picture geometry is not preserved, but that is often acceptable when, for example, the picture is formed of titles. The processing means may include means to select operation in any one of the modes.
In one embodiment described in the second earlier application, in which the storage control means includes means to select writing to and reading from the storage means, and means for generating addresses for the storage means, the address generating means is operable: (a) when writing is selected, to generate intermittently lines of addresses corresponding to part-lines of addresses in the first format; and (b) when reading is selected, to generate addresses sequentially for the field/frame of pixel data; and the storage control means is operable to discard partial lines of the pixel data of the intermediate fields/frames between the generation of one line of write addresses and the next, and to discard lines of the pixel data of the intermediate fields/frames between the generation of one field/frame of write addresses and the next. Thus, the storage means merely needs to be of a capacity such that it can store one field/frame in the second, lower definition format.
In another embodiment described in the second earlier application, in which the storage means can store a field/frame of pixel data in the first format, the address generating means is operable: (a) when writing is selected, to generate addresses sequentially for the storage means corresponding to a field/frame in the first format; and (b) when reading is selected, to generate addresses corresponding to a field/frame in the second format containing at least said part of the active portion of the intermediate field/frame.
In this case, a further such storage means may be provided, with the storage control means controlling the two storage means such that while one is being written to, the other is being read from, and vice versa. This has the advantage that, at least for some types of conversion, the apparatus can operate continuously.
The apparatus may be arranged so that when writing of the, or one of the, storage means is selected, the addresses for that storage means are generated at the pixel rate of the first format; and when reading of the, or one of the, storage means is selected, the addresses for that storage means are generated at the pixel rate of the second format. This enables real-time operation of the apparatus.
In addition to the apparatus of the second earlier application operating in a down-conversion mode, the apparatus is preferably also operable in an up-conversion mode, as described in the first earlier application, in which: the storage means stores an input field/frame of pixel data in the lower-definition format; the storage control means controls the storage means to output the stored pixel data together with dummy data as an intermediate field/frame in the higher-definition format, such that the pixel data occupies a continuous active portion of the intermediate field/frame and the dummy data occupies the remainder of the intermediate field/frame; and the processing means processes the intermediate field/frame by expanding the active portion thereof in the vertical and horizonal directions and producing an output field/frame in the higher-definition format such that the pixel data extends across substantially the whole of the output field/frame in at least one of the two directions.
The second earlier application also describes a method of down-converting a digital video signal from a first definition format to a second lower-definition format, comprising the steps of: compressing the active portion of an input field/frame in the vertical and horizonal directions to produce an intermediate field/frame in the first format in which the active portion occupies only a part of the field/frame; storing at least part of the active portion of the intermediate input field/frame of pixel data in the first format; reading the stored pixel data as an output field/frame in the second format, such that the pixel data of the active portion extends across substantially the whole of the output field/frame in at least one of the two directions.
In addition to dealing with changes in aspect ratio and resolution, the first and second earlier applications contemplate dealing with a change in field or frame rate as between the input and output video by causing the source material (such as scrolling titles, a panned background, or computer generated scenes) to move faster or slower than the rate of movement required in the converted video. The second earlier application also describes an arrangement which uses a conventional definition standards converter (for example a CCIR 601 525-lines, 60 field/s to 625-lines, 50 field/s converter) in the conventional definition portion of the apparatus in order to achieve a required change in field rate.